Eucalyptus wood samples were treated with water under selected operational conditions (autohydrolysis reaction) to obtain a liquid phase containing hemicellulose-decomposition products (mainly acetylated xylooligosaccharides, xylose and acetic acid). In a further acid-catalysed step (posthydrolysis reaction), xylooligosaccharides were converted into xylose, a carbon source for further fermentation. The kinetic pattern governing the posthydrolysis step was established by reacting xylooligosaccharide-containing liquors at 100.5 degreesC, 115 degreesC, 125 degreesC or 135 degreesC in media containing 0.5, 1.0, 1.5 or 2 wt% of catalyst (sulphuric acid). The time course of the concentrations of xylooligosaccharides, xylose, furfural and acetic acid were determined, and the results were interpreted by means of a kinetic model which allowed a close reproduction of the experimental data. Almost quantitative conversion of xylooligosaccharides into xylose was achieved under a variety of experimental conditions. The first-order, kinetic coefficient for xylooligosaccharide hydrolysis (k(1), h(-1)) varied with both temperature (T K) and molar sulphuric acid concentration (C) according to the equation Ink(1) = 36.66 + 1.00 In C - 108.0/(8.314T). The hydrolysis of acetyl groups followed a first-order kinetics. The cor responding kinetic coefficient (k(a), h(-1)) was correlated with the operational conditions by the equation Ink(a) = 26.80 + 1.18 In C -73.37/(8.314T).